Frequently Asked Questions


What is biomass?

Biomass is a renewable energy source derived from trees and crops through a process of combustion, distillation, or gasification. The most common means of converting biomass into energy is combustion. Biomass may be burned to produce hot water or steam in a boiler or hot air in a furnace for distribution throughout a building or collection of buildings.

Where can I learn more about wood as a biomass energy source?

The following websites may be helpful:


What are the benefits of using wood as a fuel in my boiler?

Many facility managers who chose to heat with wood note the lower fuel cost, stability of fuel prices, use of a local and renewable energy source, and the ability to receive donations of fuel as benefits of using this resource. Land managers benefit by having an outlet for wood generated by forest thinning operations.

The primary motivation for many facility mangers to heat buildings with wood is the lower fuel cost. Wood is often less expensive on a per-BTU basis than most other fuels typically used in boilers, including natural gas, propane, and electricity. (Coal is usually equivalent to or cheaper than wood.) In some cases, wood is locally available as a waste material and mutually beneficial arrangements can be made.

Land managers may need to remove dead or excess wood from forests to reduce the risks associated with forest fires, diseases, or invasive species. On-site burning is often the least expensive mechanism for removing this material; however, slash burning generates significant air pollution and may not be legal. In cities, residues from tree removals in the urban forest can create a very expensive wood disposal burden. In these cases, using this wood for fuel in a wood-burning boiler can represent a win-win situation.

Locally harvested wood may also represent a locally available renewable fuel source. This sustainable option is not only better for the environment than non-renewable fossil fuels, but also supports the local economy.

Additional information: The Fuels for Schools website compares the costs of wood fuels to fossil fuels and electricity.

I've already used the Wood Energy Calculator, are there other places to compare the costs of using wood fuel to fossil fuels?

The Fuel Value Calculator; published by the the USDA Forest Service, Forest Products Laboratory, and the Pellet Fuels Institute; and the University of Wisconsin Extension Service's Wood Fueled Boiler Financial Feasibility User's Manual may also be of help in evaluating your fuel options.

Wood Fuel

Where can I get wood to use as fuel?

Wood-fired heating systems can use wood pellets, wood chips, or "hog" fuel. Some wood-fired heating systems can use agricultural products such as corn. Wood fuels can be collected from forest thinning projects, from urban wood wastes (such as tree trimmings, wood pallets, and construction debris free from chemical treatments, nails, etc.), and from byproducts of the wood products industry (sawdust, wood chips, and planer shavings). Potential project developers should confirm the source and cost of wood fuel before proceeding with a project. Local wood products companies can be found on the Michigan Department of Natural Resources (MDNR) Forest Products Industry Directory or by contacting the Michigan Forest Products Specialist, Anthony Weatherspoon, at 517-335-3332 or In more urban areas, tree removal companies can be an additional good source of wood residues.

Common thinning practices result in approximately 10 tons of wood waste per acre, not including timber harvested from the site or mature trees retained on the site. If a 100-acre site were to be thinned every 25 years, the site would average 40 tons of wood residues per year (10 tons X 100 acres = 10,000 tons/25 year thinning cycle = 40 tons per year).

How important is fuel quality?

Wood fuel should be free from rocks, debris, over-sized pieces, chemical treatments, and contaminants. Burning agricultural waste may cause excessive "clinkers" due to the proportion of silica to wood biomass present in most crops.

Where can I learn more about wood residue availability in Michigan?

While no comprehensive report of Michigan's complete wood biomass resource is currently available, a number of older, source-specific, and/or regional reports can be reviewed to gain a better understanding of the potential feedstock availability:

Air Quality

Is burning wood bad for air quality?

New boilers burn wood efficiently and effectively and produce very little smoke or ash. Emissions from wood boilers are typiclaly lower in nitrogen oxides and sulphur oxides than fossil fuel boilers, but are usually greater in particulates. Wood boilers can be equipped with pollution control devices that reduce particulates to bring them as low or lower than fossil fuel boilers, but these devices will increase installation costs. See pages 29-38 of Final Report: Exploring Woody Biomass Retrofit Opportunities in Michigan Boiler Operations for more information.

The Fuels for Schools website includes an air quality link comparing wood fuel emissions to fossil fuels.

Several other sites also offer information about wood fuel emissions and air quality:

When do I need an air quality permit?

The Air Pollution Control Rules issued by the Air Quality Division of the Michigan Department of Environmental Quality include exemptions from air quality permits for wood-fired boilers less then 6,000,000 btu in size. Please review rule R336.1282 (b)(iii) or contact the Michigan Air Permits System at 517-373-7203 for more information.

Please review the United States Environmental Protection Agency website for non-attainment areas for particulate matter 2.5 microns in size (PM 2.5) in Michigan. Potential projects within the non-attainment areas are likely to require the use of a "baghouse" or electrostatic precipitator (ESP) to comply with air quality standards. The cost of a baghouse or ESP can be substantial. Potential developers should confirm all costs before proceeding with a project.

How tall does the stack need to be?

The stack height requirements vary from project to project, based upon the air shed created by the building the boiler is housed within. Air quality engineers can determine the most appropriate stack height for a project.

The State of Michigan Department of Environmental Quality Website includes links to model air flow around buildings.

Is there any assistance to help me file an air quality permit?

The Michigan Department of Environmental Quality's Air Quality Division Permit Section and the Environmental Assistance Program are hosting Monthly Air Permit Application Workshops for First-Time Applicants throughout 2008. These half-day workshops continue every month from March until December (except July and August) and will include both classroom learning and one-on-one assistance from a permit engineer. As the title suggests, this class is intended for first-time applicants, (i.e. sources who have never had to apply for an air permit before and most likely will never have to again). A unique feature of this workshop is that attendees have the opportunity to sit down with an engineer to discuss the specifics of their permit application. The goal of the training is to help first-time applicants submit an administratively complete application, which will hopefully lead to fewer questions and a quicker turn-around time. Additional information and on-line registration are available on the MDEQ's Workshop website. You can also see the workshop flyer for more details.


Does a wood-fired system cost more to operate?

Yes. In general, only modest increases in operations and maintenance costs are expected for small boilers, and greater increases are expected for larger boilers. The majority of the increase in operations and maintenance costs are associated with ash removal and resolving alarm conditions associated with oversized fuel.

The Fuels for Schools website compares the costs of operating wood-fueled heating systems.

How much does a wood-burning boiler cost?

The cost of a wood-burning boiler system depends on the amount of heat needed, the amount of additional space needed, the amount of work needed to tie the system into the existing system, and wood fuel storage needs. You can use the Michigan Wood Energy calculator to approximate the total project cost and projected savings associated with your current boiler, fuel type and fuel costs.

How much money can be saved by switching to wood as a fuel?

The amount of money that can be saved by switching from electricity or fossil fuel to wood depends on the cost to install the new system, the annual cost of the fuel you are using now, the annual cost of the wood fuel you would need, and the financing arrangements. You can estimate the amount of money that can be saved annually trying out different values in the online calculator.

One way to determine the economic value of installing a new wood boiler is considering the time it takes for the annual fuel savings to pay for the installation - this is called the payback period. Different organizations require different payback periods. Private businesses, for example, may require a payback period of 2 to 5 years. Government organizations typically tolerate much longer payback periods. Installations with payback periods greater than 30 years are usually considered poor projects.

Where can I get money to help build my project?

Many public facilities have the ability to fund wood-fired heating projects with construction funds raised from bonds, grants, low-interest loans and performance contracts.

Some wood-fired heating projects have been developed using zero-interest loans from the U.S. Department of Agriculture Rural Economic Development Loan and Grant (USDA REDLG) program. The funds are typically distributed from telephone and electric cooperatives and companies serving the region. Michigan's specialist for Rural Energy Programs, Rick Vanderbeek - (517)324-5218, also maintains a listserv of available funding opportunities.

The Climate Trust in Portland, Oregon has also provided funds linked to the offset and displacement of carbon from fossil fuel usage when wood volumes are consumed by new wood-fired heating systems.

Facility mangers might also consider integrating a wood-fired heating system project into a performance contract with Energy Service Companies (ESCOs) such as Chevron, Honeywell, Johnson Controls, McKinstry, etc.

The Michigan Biomass Energy Program can also assist potential project developers in locating other funding sources.

The following government resources may also be of help:

How was the Simple Payback determined?

The simple payback is determined by dividing the total cost of installing the new wood-burning boiler system by the estimated annual savings.

The annual fuel savings is calculated by subtracting the difference in cost between the existing fossil fuel and the projected wood fuel. The annual fuel savings is reduced by the projected increase in cost for the operations and maintenance of the wood-fired heating system. For boilers less than 2.5 mmbtu, the wood fuel is assumed to be wood pellets. For projects greater than 2.5 mmbtu, the cost of wood chips is used.


Existing 1,000,000 btu natural gas boiler --- $160,000 Total Project Cost / $2,128 Annual Savings = 75 year Simple Payback


Existing 1,000,000 btu propane boiler --- $160,000 Total Project Cost / $15,268 Annual Savings = 10 year Simple Payback

What does it mean if my Simple Payback is a negative number?

The simple payback is listed as a negative number if the projected cost of wood fuel is greater than the cost of your current fuel. The simple payback may also be listed as a negative number if the projected increase in opearations and maintenance cost combined with the projected cost of wood fuel is greater than the current combined operations, maintenance, and fuel costs.

What is the difference between Simple Payback and Annual Cash Flow?

The simple payback is determined by dividing the total cost of installing the new wood-burning boiler system by the estimated annual savings. The cash flow analysis looks not just at the simple payback of the project, but at the impact of borrowing money to finance the project and the impact of the project financing on the overall cash flow.

For example, if a facility manager borrows $648,500 at 5% financing for 10 years, the annual payment to the lending institution would be $84,000, negating a potential $64,850 year one savings for the project. This deficit can only be overcome by accounting for the impact of inflation on the existing heating costs (fuel, operations, and maintenance) and wood-fired heating system costs (fuel, operations, and maintenance). In general, existing heating system costs escalate at a more rapid rate than locally available and renewable sources of fuel such as wood. Thus, over time, positive cash flow is achieved in spite of negative cash flow during the first few years of a project. Positive cash flow can also be enhanced with grants or low-interest loans.

Project Details

Why does the web-based calculator assume that a wood-fired boiler would be half the size of my existing boiler?

In general, fossil fuel boilers are sized to meet peak load conditions which occur infrequently and for very short durations (such as for 15 minutes every five years).

If a wood-fired boiler were to be sized to meet the peak load condition it would frequently operate in low and medium fire conditions. Unlike fossil fuel boilers which modulate well between high, medium, and low fire, wood-fired boilers perform most effectively in high fire mode. By reducing the size of the wood-fired boiler, it will operate in high fire mode more often. An energy model should be developed to determine the optimal size of the wood-fired boiler. Generally, this size meets 90-95% of a typical heat load. Existing fossil fuel boilers can be used to meet low load and peak load conditions as necessary.

How long will it take to complete my project?

Most projects take 12-18 months to develop from initial feasibility study through system start-up and operation.

A typical project schedule should include one month for a preliminary assessment, two months for a detailed engineering study, six months to develop the system design, one month to bid, and six months to construct. The boiler may take between 3-9 months to construct. A one-year warranty period should include quarterly training sessions to assist staff in troubleshooting the operation of the system under various weather conditions.

Why is energy conservation important?

Energy conservation projects are likely to reduce the total volume and cost of all needed fuels. Conserving energy assures that renewable resources will be used more effectively. However, conserving energy is likely to also reduce the amount of fossil fuel used in an existing system, thus reducing the simple payback for a wood-fired heating system.

If wood is cheaper than your current fuel, then the more fuel you currently use, the more economically attractive it will be to switch to a wood-burning boiler. However, facilities may be able to save as much or more in fuel costs by taking steps to conserve energy by doing things such as improving boiler controls. In some cases, conserving energy can reduce existing fuel costs to the point where the fuel cost savings generated by switching to wood do not generate desirable payback periods. For these reasons, it is recommended that you do an energy audit on your building to determine the economics and results of energy conservation measures before or while considering the costs and benefits of installing a wood boiler.

What about my existing distribution system and controls?

In most cases, the existing heat distribution and controls systems will remain unchanged. It is important to convey to the engineering team how you operate your existing system and to describe in detail any problems you have had with the quality and quantity of heat in your facilities.

Modern wood-fired heating systems rely upon sophisticated control systems in order to conserve heat and reduce emissions. Most wood-fired heating system control panels can be designed to interface with existing building controls.

What about power generation?

Many wood-fired boilers are used to produce steam for both heat and power and are referred to as combined heat and power systems (CHP). Most CHP projects have incorporated a steam host such as a mill or hospital that needs a consistent source of steam for heat or industrial processes. The greater the steam flow (measured in pounds per hour), the more power can be generated. Many users produce power for on-site needs and to offset demand charges for power from the grid.

The National Renewable Energy Website and Turbosteam websites provide additional resources for project developers.

Success Stories

Where can I learn more about successful wood biomass energy projects?

Here are a few case studies that may be of interest: